Overpressure conditions can lead to a variety of disasters—injuries, damaged equipment, business interruptions and downtime. An explosion can result from an ignition of a combustible gas, mist or dust when mixed with air during processing, handling or storage operations. In closed spaces containing electrical apparatus an explosion may be caused by an electric arc initiated by damage or failure of the apparatus or circuitry. At explosion, a rapid rise in pressure occurs in the containing structure, and if it is not of adequate strength to withstand the deflagration pressure, extensive damage and injury to personnel can occur. For these reasons it is paramount to provide controlled pressure release for spaces where a danger for explosion exists.
When an explosion is vented, the overpressure built up in closed space like cabinets or the plant itself is directly vented to the outside or any desired safe direction. This protects plants and containers from possible shock waves that, in turn, could cause complete destruction.
Controlled venting of a closed space can be accomplished by an opening formed on a wall of a cabinet or other closed space and closing it by a cover. The cover extends over the edges of the opening and a seal is placed around the opening in order to achieve desired tightness for fluids like gases and liquids. The cover may be attached to the cabinet wall by screws. The cover is dimensioned to rupture under specific pressure and when ruptured, it forms a venting hole for pressurized substances within the cabinet.
An alternative solution is to make a weakened or relieved area on the structure of the closure. This is used especially for cast frames and bodies wherein a wall section that is thinner than load bearing walls is placed in a suitable location.
One alternative is to form an opening in the structure and close that by a rubber plug that is formed to fit in the hole and close it tightly.
Explosion venting becomes also possible when special explosion protection panels (bursting discs) are installed. A bursting disc (also known as a rupture disc or bursting disk), is designed to provide a leak-tight seal within a pipe or vessel, until the internal pressure rises to a predetermined level. At that point the bursting disc ruptures, preventing damage to the equipment from overpressure. This type of explosion vents are low burst pressure membranes of calculated area fixed over an opening on the structure to be protected. In the event of a deflagration the vents provide a rapid and unrestricted opening at a predetermined burst pressure (Pstat) allowing combustion gases to expand and flow through the open vent. The required relief area necessary to protect plant or equipment may be determined by using the most current standards of NFPA 68 or VDI 3673.